Evaluate the following expression when $y = 4$ and $x = 6$. $6$ $y$ $ + 3$ $x$ $ + 9$
Solution: Substitute $4$ for ${y}$ and $6$ for ${x}$ $ = 6{(4)} + 3{(6)} + 9 $ $ = 24 + 18 + 9 $ $ = 51$